Land Mobile Radio (LMR) systems are deployed by organizations requiring instant communication between geographically dispersed and mobile personnel. Typical users of LMR systems include police departments, fire departments, medical personnel, EMS and the military.
Current LMR systems can be configured to provide for radio communications between a site and subscriber units in the field. A subscriber unit may be a mobile unit or a portable unit. LMR systems can be as simple as two subscriber units communicating between themselves and a site over preset channels, or they can be complex, consisting of hundreds of subscriber units and multiple sites.
LMR systems may be configured to cover a large geographical area by providing hundreds of sites. In centralized/switched LMR systems, calls between sites are setup through one or more centralized switches. Devices can be analog or digital. In contrast, calls involving multiple sites are setup by the sites directly, without the use of centralized switches or equivalent, using digital networks, in particular IP networks, where the calls are carried using Voice Over Internet Protocol (VOIP) technology.
Users of the LMR system are divided into groups. Users in a group can talk to one another using their radios. Dispatchers can interface with the LMR systems utilizing a computer having speakers and a dynamic graphical display. Dispatchers can select one of several predefined groups of users, and talk to the selected group. Members of the groups can talk to one another.